Trunk muscle activity during holding two types of dynamic loads in subjects with nonspecific low back pain

Background: Chronic low back pain due to manual lifting continues to be one of the significant common public health challenges in modern societies despite increased automation. While there are extensive studies on the biomechanics of lifting as associated with LBP, the role of unstable and time-varying dynamic loads, quite common in industrial lifting and daily life, remains elusive. Objectives: The present study aimed to investigate the response of trunk muscles in subjects with chronic non-specific low back pain (CNLBP) while holding unstable dynamic loads. Methods: Twelve male patients with CNLBP and twelve healthy controls participated in this cross-sectional study. The subjects held static and dynamic loads in neutral positions. Normalized EMG data of the trunk muscles were captured and analyzed by repeated-measures ANOVA test. Results: The low back pain group demonstrated significantly higher activation levels of the internal and external abdominal oblique muscles while holding dynamic loads (p < 0.05). Conclusion: Our results suggest that the neuromusculoskeletal system in low back patients holding dynamic loads may invoke a motor control strategy that significantly increases muscle co-activation leading to higher joint stiffness at the expense of higher compressive loads on the lumbar spine. Importantly, the type of load plays a critical role in terms of external perturbations that may lead to spinal injury in CNLBP patients and must, therefore, be considered in the risk prevention and assessment of lifting and other manual material handling tasks.